The U.N. human rights office said Islamic State militants are increasing mass killings and abductions of civilians to use as human shields as the battle for Mosul in Iraq intensifies.

The Office of the High Commissioner for Human Rights said Islamic State militants are continuing to forcibly transfer civilians to the city of Mosul and its outskirts to shield themselves from air strikes.

Over the past few days, it said s about 2,500 civilians were abducted from the town of Hamam al-Alil, with some people were being told they would be transported to Syria. The agency said it also continues to receive reports of mass killings.

Human rights spokeswoman Ravina Shamdasani said last Monday IS, also known as ISIL, reportedly killed 50 of its own militants in the Ghazlani military base in Mosul for alleged desertion.

She said there also are credible reports of 380 people being killed on Wednesday in Mosul and the nearby town of Kokjali. “We have reports that ISIL militants are holding captive nearly 400 women from Kurdish, Yazidi or Shi’a Muslim communities in Tal Afar."

"We do not know how many of them belong to which of these minority groups ," added Shamdasani. "But, we are obviously very, very concerned because these are particularly vulnerable populations. They are women, they are minorities, and we are very worried about what might transpire.”

Islamic State defensive preparations in the city of Mosul are pictured ahead an impending battle with Iraqi troops in this Oct. 31, 2016 satellite handout photo.

Shamdasani said IS reportedly also has been forcibly recruiting very young children to fight in Mosul since the Iraqi government operation to retake the city began October 17.

“We do not have the exact numbers," said Shamdasani. "But, what we do know is that ISIL has been ordering the residents of Hamam al-Alil city, for example, to hand in, to surrender all children who are aged at least nine or 10 to the group. And, apparently, they have also been using loud speakers mounted at the back of pick-up trucks or the back of vehicles and threatening severe punishment for families that do not comply with their order.”

The U.N. agency said it has received reports of civilians killed by airstrikes, including one on Wednesday that reportedly killed four women and wounded 17 other civilians in a neighborhood in eastern Mosul.

The agency is calling on the Iraqi government and its allies to conduct military operations in accordance with international humanitarian law and to take precautions to avoid and minimize loss of civilian life.